The present invention relates generally to speakers and, more particularly, is directed to ported speakers.
Speakers, or loudspeakers, are well known and are commonly used in a wide variety of applications, such as in home theater stereo systems.
Speakers typically comprise a hollowed out cabinet, or box, which is commonly manufactured of plywood, particle board or medium-density fiberboard. Various electrical components, such as a crossover, an L-pad and a terminal cup, are disposed within the cabinet and are electrically connected to an amplifier for the stereo system. One or more speaker units, such as tweeters and woofers, are positioned and sealed within associated holes formed into the surface of the cabinet. The speaker units are electrically connected to the electrical components of the speaker and vibrate in response to electrical inputs to produce sound.
Speaker cabinets are often manufactured using the following technique. An elongated strip of vinyl-laminated particle board having a first end and a second end is cut at predetermined locations. The elongated strip is then folded at the cut portions and the first and second ends are sealed together to form a four-sided, box-shaped configuration having an open top, an open bottom and an internal box cavity. A rectangular top panel and a rectangular bottom panel are permanently mounted on opposite sides of the elongated strip to enclose the internal box cavity.
One drawback of speaker cabinets manufactured in the manner noted above is that the final closure point of the first end of the elongated strip to the second end has often been found to be inadequately sealed. As a result, regions of the cabinet may vibrate which, in turn, produces noise, which is undesirable. In order to eliminate the vibratory noise, the inadequately sealed portion of the cabinet must be resealed air tight. This resealing process is typically a time-consuming and costly procedure.
In the art of speaker design, engineers are constantly striving to maximize speaker acoustical performance while, at the same time, minimize overall speaker size. In particular, it is a common object in the art to improve the range and quality of low frequency, or bass, sounds without greatly increasing the overall size of the speaker.
In order to produce stronger and deeper bass frequencies without increasing overall speaker size, it is well known in the art to provide a port in the cabinet of the speaker. A port is generally an open duct which includes a sound path that communicates the internal box volume of the cabinet with an external portion of the cabinet. Ported speakers, also commonly referred to as bass-reflex, vented, or phase-inverted speakers, have a resonant frequency which is defined by the air spring of the internal box volume of the cabinet and the air mass in the sound path of the port. At frequencies higher than the resonant frequency, the sound passing through the sound path is inverted and the sound emitted from the driver is in-phase. The two sounds are in-phase added to one another to increase sound pressure. As a result of the in-phase addition, the low frequency characteristics of the output sound pressure are expanded.
The frequency characteristics of ported speakers are directly attributable to the cross-sectional area of the sound path of the port, the length of the neck of the port and the internal box volume of the cabinet. By balancing the dimensions of the port and cabinet of the speaker, the acoustical performance of the speaker can be maximized without significantly increasing the overall size of the speaker, which is desirable.
Although ported speakers are well-known and commonly used in the art, they nonetheless experience noticeable drawbacks.
As a first drawback, the implementation of a port into the cabinet of a speaker requires additional steps in manufacturing, which thereby increases the total cost of the speaker.
As a second drawback, it has been found that an open duct resonance, wind noise, turbulence, or the like often occurs at the port. Specifically, a port of considerably narrow cross-section causes air which passes therethrough to move at a high speed. The high speed of the air passing through the port, in turn, collides against the edge portion of the port at the portion where the air flow passing through the port cannot become uniform, e.g., the small diameter portion or openings at two ends of the open duct port, thus causing wind noise or turbulence.
In U.S. Pat. No. 5,109,422 to K. Furukawa, there is disclosed an acoustic apparatus comprising a Helmholtz resonator which has a cavity and an open duct port for causing the cavity to communicate with an external region thereof and a vibrator which is arranged in the resonator to drive the resonator. In a first aspect, the open duct port comprises an air permeable member having a proper acoustic and resistance and a viscoelastic member having no air permeability so that noise caused by an open duct resonance, wind noise, turbulence or the like is prevented. In a second aspect, a viscoelastic member is disposed at the mounting portion between the open duct port and a cabinet defining the cavity so that transmission to the cabinet of derivative vibration caused at the open duct port is prevented. In a third aspect, the portion, opposite to the open duct port, of an ornament grille attached to the front surface of the acoustic apparatus is given a larger air permeability than other portions of the grille so that wind noise when the grille is attached before the open duct port is prevented. Thus, noise generated when the resonator is driven is prevented or eliminated and distortion characteristics of the apparatus are improved.
In U.S. Pat. No. 5,606,626 to C. H. Kim et al, there is disclosed a speaker system with an anion generator and a television set using the speaker system. The speaker system includes an anion generator provided within a speaker box. Sound pressure is used to help spread the generated anions outside the speaker box. An antistatic agent may optionally be provided on one or more surfaces of the speaker box to prevent static charge build-up within the speaker box.